media/gpu: Add mojo/edk initialization to unittest.

This adds mojo/edk initialization to
media/gpu/video_decode_accelerator_unittest. This is necessary for
future changes that use mojo machinary for shared memory manipulation.

Bug: 849207
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel
Change-Id: I6d04891a4d306f7c458eb2bb4ce3fd42a1b77759
Reviewed-on: https://chromium-review.googlesource.com/1122095
Commit-Queue: Matthew Cary <mattcary@chromium.org>
Reviewed-by: Pawel Osciak <posciak@chromium.org>
Reviewed-by: Ken Rockot <rockot@chromium.org>
Cr-Commit-Position: refs/heads/master@{#576121}

media/gpu/BUILD.gn

@@ -387,6 +387,7 @@ if (is_win || is_android || use_v4l2_codec || use_vaapi) {
         "video_decode_accelerator_unittest.cc",
       ]
       deps += [
+        "//mojo/core/embedder",
         "//ui/display",
         "//ui/display/types",
         "//ui/platform_window",

media/gpu/DEPS

 # Do NOT add net/ or ui/base without a great reason, they're huge!
 include_rules = [
+  "+mojo/core/embedder",
   "+services/service_manager/public",
   "+third_party/angle",
   "+third_party/libyuv",

media/gpu/video_decode_accelerator_unittest.cc

@@ -67,6 +67,7 @@
 #include "media/gpu/test/video_accelerator_unittest_helpers.h"
 #include "media/gpu/test/video_decode_accelerator_unittest_helpers.h"
 #include "media/video/h264_parser.h"
+#include "mojo/core/embedder/embedder.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "ui/gfx/codec/png_codec.h"
 #include "ui/gl/gl_image.h"
@@ -1591,6 +1592,8 @@ class VDATestSuite : public base::TestSuite {
 
   int Run() {
 #if defined(OS_WIN) || defined(OS_CHROMEOS)
+    mojo::core::Init();  // Required only for Win7 tests.
+
     // For windows the decoding thread initializes the media foundation decoder
     // which uses COM. We need the thread to be a UI thread.
     // On Ozone, the backend initializes the event system using a UI